This application claims the priority of Japanese Patent Application No. 3-181366 filed on Jul. 22, 1991, which is incorporated herein by reference.
1. Field of the Invention
The present invention generally relates to a wiper controller for controlling a wiper used in a vehicle. More particularly, the present invention is directed to a wiper controller which drives the wiper intermittently.
2. Description of the Related Art
A conventional wiper controller is capable of selectively setting a fast wiping mode, a slow wiping mode, and an intermittent mode for intermittently moving the wiper at predetermined intervals. Several wiper controllers have been developed to control the intermittent inactive time of the wiper when the intermittent mode is selected.
Japanese Unexamined Patent Publication No. 60-189664 discloses such a wiper controller which is capable of setting the inactive time in the intermittent wiper action to an arbitrary value within a few seconds. This wiper controller comprises a control processor, a variable resistor and a multivibrator circuit. The multivibrator circuit has a plurality of resistors and capacitors, as well as at least two transistors which are alternately turned on and off based on an input signal to the multivibrator circuit. The multivibrator circuit outputs a signal having a pulse width corresponding to the set value of the variable resistor. The control processor controls the intermittent action of the wiper based on that output signal.
FIG. 9 of the drawings shows another conventional wiper controller. This wiper controller includes a control processor 21, a variable resistor 22, and an oscillation circuit 20. The oscillation circuit 20 comprises a plurality of resistors, capacitors and transistors, and outputs a pulse signal having a predetermined waveform. The control processor 21 controls the intermittent action of the wiper based on the output signal. When the variable resistor 22 is adjusted, the period of the pulse signal output from the oscillation circuit is changed, thereby altering and setting the intermittent inactive time of the wiper.
However, both types of conventional wiper controllers require a relatively large number of electronic components to form the multivibrator circuit or the oscillation circuit 20. In addition, the latter type, which is equipped with the oscillation circuit 20 suffers the unstable oscillation frequency of the output signal of the oscillation circuit 20, as well as from the difficulty in setting a constant oscillation for the oscillation circuit 20. This inevitably results in a large variation in the intermittent inactive time of the wiper, and disables the intermittent wiper action at accurate time intervals.